Changing sediment yield as an indicator of improved soil management practices in southern Brazil

Catchment-level soil and water conservation programmes have been widely employed in Brazil. An important component of these programmes is the implementation of water and sediment monitoring projects to evaluate the impact of changes in soil management on water resources. In general, results from monitoring projects have been inconclusive, due to a series of difficulties associated with data collection and limited timeframes. This study presents results from a hydrosedimentological monitoring project undertaken in a small (1.19 km²) rural catchment in Southern Brazil before and after the introduction of conservation tillage practices implemented by the RS-RURAL — Program Against Rural Poverty. These practices, including use of winter cover crops and minimum tillage tobacco cultivation, were gradually adopted by local farmers. Data on precipitation, runoff volume, maximum flow and sediment yield were assembled for representative storm events occurring between May 2002 and March 2006, and analyzed to identify changes in the storm runoff and storm-period sediment response of the study catchment. The results provide evidence of statistically significant reductions in storm runoff, maximum flow rate and sediment yield after implementation of the conservation practices. Sediment sources were also investigated using the fingerprinting technique and this work demonstrated a statistically significant reduction over the study period in the proportion of the sediment contributed by fields (62% to 54%) and unmetalled roads (36% to 24%). This reduction was offset by an increased contribution of sediment from channel sources (2% to 22%). The increased proportion of sediment mobilized from the channel is in part a function of the reduced contribution from the two other sources, but it also reflects the reduction in sediment inputs to the channel from the fields and unmetalled roads, which results in an increase in the energy available for channel scour. Results emphasize the complexity of the relationship between sediment yield, the effects of climactic variability, and changes in land use and management.     

Impact of no-tillage agricultural systems on sediment yield in two large catchments in Southern Brazil

Purpose

The impact of agriculture on water resources has long been a problem associated with the formation of runoff, the siltation of lakes and reservoirs, and overall depletion of water quality. In Brazil, these problems are mainly related to soil degradation by water erosion. However, studies of catchment-scale erosion are still rare particularly in grain-producing regions which have adopted conservative tillage systems for soil protection. In order to contribute to a better understanding of the impact of conservation agriculture on water resources, this study determined the runoff coefficient and sediment yield for two agricultural catchments.

Materials and methods

Hydrological and sedimentological monitoring was conducted in two catchments: the Conceicao catchment is characterized by grain production in weathered soils and a gently sloping landscape, while the Guapore catchment is characterized by heterogeneous soils and topography. Both catchments have problems associated with water erosion.

Results and discussion

The magnitudes of annual runoff coefficients and sediment yield were high, even if compared to similar agricultural regions, including a catchment with widespread adoption of no-tillage. The sediment yield was 140 t km^?2 year^?1, and the runoff coefficient was 14 % for the Conceicao catchment, while the sediment yield was 270 t km^?2 year^?1, and the runoff coefficient was 31 % for the Guapore catchment. The results indicate that problems such as gullies, soil compaction, runoff, floods, siltation, and water quality depletion associated with the misuse of agricultural areas in terms of soil conservation and water use are still evident and important even in regions with widespread adoption of no-tillage systems.

Conclusions

The magnitudes of both runoff and sediment yield clearly indicate the need to adopt complementary practices of soil conservation measures, such as mechanical runoff control.     

坡度对农业耕作措施水土保持作用的影响

农业耕作措施是水土保持三大措施之一,在坡耕地水土保持中起关键作用。利用人工模拟降雨试验方法,对不同坡度条件下农业耕作措施水土保持作用进行了研究。农业耕作措施包括等高耕作、人工掏挖和人工锄耕,以平整坡面为对照措施;降雨试验在长4m,宽1m的径流小区完成;坡度为5°,10°,15°,20°,25°;降雨强度为1,1.5,2mm/min。结果表明:与平整坡面相比,等高耕作、人工掏挖和人工锄耕分别减小产流量38.19%,32.25%和15.84%;减小产沙量均在50%以上,说明农业耕作措施具有明显的水土保持作用。通过对坡度与产流量、产沙量关系分析表明,在耕作坡面,坡度会影响产流量,但是大坡度与小坡度之间差异不显著。相反,坡度对产沙量具有显著影响,在小坡度条件下,产沙量受坡度的影响较小。当坡度大于15°后,坡度每增加1°,等高耕作、人工掏挖和人工锄耕耕作措施保土作用平均降低3.08%,4.74%和7.61%。回归分析表明产沙量与坡度之间存在指数函数关系。可见,坡度对农业耕作措施保水作用和保土作用的影响不同。     

耕作对坡耕地水土流失和冬小麦产量的影响

在模拟降雨和自然降雨条件下研究长期（6年）定位耕作措施对豫西早区坡耕地水分保持、土壤流失以及冬小麦产量的影响。耕作措施包括少耕、免耕覆盖、深松覆盖和常规耕作。田间模拟降雨试验用来测定不同耕作措施对径流和土壤流失的影响，自然降雨小区主要用来验证模拟试验结果，同时测定不同耕作措施对冬小麦产量的影响。模拟试验结果表明：不同耕作措施下的土壤饱和导水率没有明显差异，雨前土壤含水量和降雨强度均显著影响地表径流。在试验条件下，免耕覆盖处理未产生径流和土壤流失，水土保持效果最好。与常规耕作比较，深松覆盖处理分别减少径流和土壤流失50％和90％。尽管少耕可以有效降低土壤流失，但其产生的径流量和常规耕作相近。在自然降雨条件下，免耕覆盖和深松覆盖的水土保持效果从第3年开始显著。深松覆盖在任何年型均能够显著提高冬小麦的产量。相比较常规耕作，深松覆盖平均增产9．4％。免耕覆盖除丰水年也能显著提高冬小麦产量．但增产效果不如深松覆盖显著。少耕无明显增产效果。由于产量对农民来说是评判一个耕作措施效果的重要依据，同时考虑到深松覆盖显著的水土保持效果，我们认为深松覆盖是适合当地早作农业的一个有效耕作措施。     

红壤小流域不同利用方式水土流失和有机碳流失特征研究

研究了红壤小流域不同利用方式的试验区水土流失和有机碳流失的特征 ,结果表明 :径流、泥沙及有机碳流失主要集中在 5月、6月及 8月份 ,其间径流流失量占全年流失量的 68.8%～ 73 .1 %,泥沙流失量和有机碳流失量占全年流失量的 90 %以上。径流量和泥沙流失量的大小顺序均为无保护性措施、侵蚀严重的试验区 5>粗放经营利用的试验区 1 >保护性经营利用试验区 2 >保护性经营利用试验区 4>恢复保护性植被试验区 3 ;流失的泥沙主要为推移质 ,有机碳流失量的大小顺序为粗放经营利用的试验区 1 >保护性经营利用的试验区 2 >保护性经营利用的试验区 4>无保护措施、侵蚀严重的试验区 5>恢复保护性植被的试验区 3 ,径流流失的有机碳和推移质流失的有机碳基本接近。从保护资源角度来看 ,恢复保护性植被试验区 3的利用方式控制水土流失和有机碳的效果最好。从农林利用角度来看 ,以有保护性经营利用综合性措施 (等高梯田、植被篱笆、农林间作等措施 )的试验区 2和试验区 4利用方式 ,既有利于水土保持 ,又有利于防止土壤肥力下降     

黑土坡耕地不同水土保持措施的土壤水蚀特征研究

针对北方干旱地区坡耕地严重的水土流失问题,采取垄向区田、深松、横坡种植、免耕播种等水土保持耕作措施,于2010年,以黑龙江省齐齐哈尔市东兴村5°坡耕地径流场为研究对象,研究了不同耕作措施对地表径流、土壤侵蚀和降雨入渗的影响。结果表明,这几种水土保持耕作措施均有不同程度的减流减沙作用,其中横坡种植效果最为明显,地表径流量和土壤流失量较常规耕作分别减少了92%和90%,稳定入渗率较常规耕作提高了41.2%。不同耕作措施的径流系数过程线的变化、径流含沙率变化以及产流量、产沙量的变化均符合横坡免耕>横坡种植>深松+区田>垄向区田>少耕深松>免耕>常规耕作>裸地这一变化规律。     

小流域径流泥沙自动采集器的试验研究

仪器仪表作为对信息进行采集、测量、处理和控制的重要手段和设备,已成为推动科学技术和国民经济高速发展的关键技术之一。在小流域出口处设置量水堰是研究流域水文过程及土壤侵蚀监测的一个重要方法,为实现小流域径流含沙量的动态监测,自行研制了一种小流域径流泥沙自动采集器,以一种简单的采样技术代替传统方法来提高含沙量测定的自动化水平及测量精度。通过模拟试验验证了采集器的适用性,结果证明采集器具有很好的可靠性和观测精度,与标准值的平均相对误差仅为0.42%。另外,该装置与传统水样收集方法相比自动化程度高,管理方便,适于野外无人看守情况下径流样品的自动采集。因此,所研制的小流域径流泥沙自动采集器有一定的应用前景。     

Soil management effects on runoff and soil loss from field rainfall simulation

Soil erosion from agricultural lands is a serious problem on the Chinese Loess Plateau. In total, 28 field rainfall simulations were carried on loamy soils under different management practices, namely conventional tillage (CT), no till with mulch (NTM), reduced tillage (RT), subsoiling with mulch (SSM), subsoiling without mulch (SS), and two crops per year (TC), to investigate (i) the effects of different soil management practices on runoff sediment and (ii) the temporal change of runoff discharge rate and sediment concentration under different initial soil moisture conditions (i.e. initially dry soil surface, and wet surface) and rainfall intensity (85 and 170 mm h^− 1) in the Chinese Loess Plateau. NTM was the best alternative in terms of soil erosion control. SSM reduced soil loss by more than 85% in 2002 compared to CT, and its effects on runoff reduction became more pronounced after 4 years consecutive implementation. SS also reduced considerably the runoff and soil loss, but not as pronounced as SSM. TC resulted in a significant runoff reduction (more than 92%) compared to CT in the initial ‘dry’ soil, but this effect was strongly reduced in the initial ‘wet’ soil. Temporal change of runoff discharge rate and sediment concentration showed a large variation between the different treatments. In conclusion, NTM is the most favorable tillage practices in terms of soil and water conservation in the Chinese Loess Plateau. SSM can be regarded as a promising measure to improve soil and water conservation considering its beneficial effect on winter wheat yield.     

降雨类型对褐土横垄坡面土壤侵蚀过程的影响

雨型是影响土壤侵蚀过程的重要因子之一,而影响效应与耕作措施密切相关。目前,雨型对横垄坡面土壤侵蚀过程的影响机制尚不清楚。该文以褐土横垄坡面为研究对象,设计了平均雨强和降雨量相同的4种雨型(增加、减弱、增加-减弱和减弱-增加型),采用可同时调节垄向和坡面坡度的土槽进行模拟降雨,研究各个雨型下不同侵蚀阶段的产流产沙特征。结果表明:雨型间的径流量和侵蚀量在细沟间和细沟侵蚀阶段均差异显著,且差异在细沟阶段体现的更为明显。雨型间径流量的大小顺序为增加-减弱型减弱型减弱-增加型增加型,侵蚀量则为增加-减弱型减弱-增加型减弱型增加型。给定雨强下(30、60或90 mm/h),径流量、径流贡献率和侵蚀量贡献率均随降雨过程中雨强发生时序的延迟而增加,而单位径流侵蚀量呈相反趋势;雨型间给定雨强同一发生时序下的径流量和侵蚀量及其它们对总径流量和总侵蚀量的贡献率均差异显著。4种雨型下,幂函数均能很好的描述细沟间和细沟侵蚀阶段内产沙率与径流率间的关系,且方程中的指数均低于2,但雨型间幂函数方程中的指数存在明显差异。以上研究结果有助于深入理解褐土垄作系统下的土壤侵蚀机理,并为横坡垄作的合理利用提供科学指导。     

Tracing Sediment Sources Using Mid‐infrared Spectroscopy in Arvorezinha Catchment,Southern Brazil

The widespread adoption of the sediment fingerprinting approach to guide catchment management has been limited by the cost and the difficulty to prepare and process samples for geochemical and radionuclide analyses. Spectral properties have recently been shown to provide a rapid and cost‐efficient alternative for this purpose. The current research objective was (i) to quantify the sediment source contributions in a 1∙19‐km² rural catchment of Southern Brazil by using mid‐infrared (MIR) spectroscopy and (ii) to compare these results with those obtained with geochemical approach and near‐infrared and ultraviolet–visible spectroscopy methods. The sediment sources to discriminate were cropland surface (n  = 20), unpaved roads (n  = 10) and stream channel banks (n  = 10). Twenty‐nine suspended sediment samples were collected at the catchment outlet during nine significant flood events. The sources could be distinguished by MIR spectroscopy. Cropland and channel bank sources mainly differed in their clay mineral contents, but their similar organic matter content complicated the MIR‐model predictions. Unpaved road contributions were discriminated from the other sources by their lower organic carbon content. When the results of the current research based on MIR spectroscopy are compared with those obtained using other sediment fingerprinting approaches, based on geochemistry and near‐infrared and ultraviolet–visible spectroscopy, an overestimation of channel banks contribution and an underestimation of cropland and unpaved road contributions is found. These results suggest that MIR spectroscopy can provide a useful tool that is non‐destructive, rapid and cheap for tracing sediment sources in rural catchments and for guiding the implementation of soil and water conservation measures. Copyright © 2016 John Wiley & Sons, Ltd.     

不同耕作措施下成熟期玉米对径流及侵蚀产沙的影响

采用野外人工模拟降雨的方法,开展不同耕作措施下成熟期玉米对坡面产流及产沙影响的研究。结果表明:不同雨强下,种植玉米各措施径流量和产流强度都要小于相应的对照。在雨强为1.0,2.0mm/min下,平作措施径流量最小;在雨强为1.5mm/min下横坡措施径流量最小;在雨强为1.5mm/min下,平作措施和顺坡措施径流量达最大。在雨强为1.0mm/min下各措施含沙量均最小;在雨强为1.5mm/min下平作措施含沙量达最大;在雨强为2.0mm/min下横坡和顺坡措施含沙量最大。不同雨强下,平作、顺坡耕作、横坡耕作和对照小区产流产沙过程均呈波动变化,平作、顺坡耕作和横坡耕作的产流时间均较对照小区延后。     

Arkansas Discovery Farms: documenting water quality benefits of on-farm conservation management and empowering farmers

Arkansas Discovery Farms (ADFs) are private farms that collaborate with on-farm research, verification, and demonstration of farming's impact on the environment. We have nine ADFs representing livestock (broiler poultry and pasture grazed beef and sheep) and row crop agriculture (corn, cotton, rice, soybean, and wheat), where we collect water use and water quality data as a function of conservation management, using autosamplers equipped with edge-of-field H-flumes or weir flow structures, which measure and collect surface runoff. On the poultry farms, we are monitoring nutrient and sediment runoff originating immediately near poultry houses due to concerns with spillage of litter during bird removal and house clean out, as well as dust from tunnel ventilation. On a nearby farm we are assessing the impact of rotational grazing on water quality, soil organic matter, and soil health metrics. On the row crop farms we are assessing the impacts of conservation tillage and cover crops on soybean–corn rotations and cotton on nutrient and sediment runoff and the benefits of water harvesting and reuse of water conservation and quality. The information in this paper while preliminary, demonstrates how a state-wide on-farm demonstration program operates. Elevated nutrient and sediment runoff from around poultry production areas are decreased three-fold by directing runoff into ponds or through grassed waterways. While conservation tillage and cover crops do decrease nutrient and sediment runoff, no significant difference between conventional and conservation operations is yet to be realized. Importantly, ADF empowers farmers to proactively address environmental concerns. This paper discusses the development, guidance, principals, and goals of ADF and contrasts this with other farm monitoring projects, where the sources of nutrient impairment are the subject of ongoing litigation. Monitoring in divisive and transparent situations presents unique challenges with data ownership and release of findings, which can hinder productive outcomes of such monitoring.     

不同耕作措施对花生结荚期产流产沙过程的影响

为了研究不同耕作措施在花生结荚期时对紫色土区产流产沙过程的影响,通过对顺坡垄作、横坡垄作、穴播、平作这4种耕作措施种植花生以及对照组平坡裸地进行野外模拟降雨试验,得到其径流泥沙特征。利用滑动秩和检验法找出产流产沙过程变异时刻点,对变异时刻点后用Mann-Kendall趋势检验法分析产流产沙过程趋势。结果表明:产流产沙过程变异时刻点后均处于一个较为稳定状态,平坡裸地的稳定径流率、侵蚀率均最大,顺坡垄作次之,然后是平作,再是穴播,横坡垄作最小;而各耕作措施初始产流时间则与稳定径流率和侵蚀率相反。在减流减沙效益方面,相对于平坡裸地,不同耕作措施均表现出减流减沙效果,具体表现为横坡垄作>穴播>平作>顺坡垄作。     

垄作方式对薄层黑土区坡面土壤侵蚀的影响

定量评价垄作方式对坡面土壤侵蚀的影响,可为坡面土壤侵蚀防治提供理论参考。基于2012—2015年哈尔滨市野外径流小区监测资料,探讨了顺坡垄、横坡垄、无垄作(裸地休闲对照)垄作方式对坡面土壤侵蚀的影响,分析了不同垄作方式下坡面水沙关系。结果表明:不同垄作方式下径流量和侵蚀量均具有显著差异,坡面径流量和侵蚀量均表现为无垄顺坡垄横坡垄;与无垄作试验处理相比,横坡垄作使坡面径流量和侵蚀量平均减少了92.4%和98.3%,顺坡垄作使坡面径流量和侵蚀量平均减少66.4%和72.2%。当坡度由3°增加到5°时,无垄作、顺坡垄作、横坡垄作坡面侵蚀量分别增加了0.8,8.2,5.5倍。3种垄作方式下坡面水沙关系均呈现出良好的相关关系,顺坡垄作和无垄作坡面侵蚀量随径流量的增加幅度远大于横坡垄作坡面,当坡面径流量10.0mm时,二者坡面侵蚀量急剧增加。     

黄土高原坡面水土保持措施减沙水代价分析

不同的水土保持措施在减少侵蚀泥沙的同时对径流量的影响不同.以裸坡地水土流失为对照,分析了不同水土保持措施减水减沙比(Rrs),并以其作为减沙水代价指标,根据黄土高原土壤侵蚀严重的丘陵沟壑区(西峰、绥德、天水等3个典型区)的农地径流小区多年观测资料,分析了不同耕作措施及生物措施的减沙水代价(Rrs).结果表明,不同耕作方式Rrs差异很大,变化幅度在8.5～36.4 m3/t;在耕作措施上,横向耕作的Rrs大于防冲沟和浅耕,深耕Rrs最小;生物措施方面,低秆与高秆作物间作措施Rrs大于单作低秆作物和中高秆作物轮作,牧草(草木樨、苜蓿)轮作的Rrs较农作物轮作大,且草木樨与农作物轮作的Rrs大于苜蓿与农作物轮作.随着雨量的增加和坡度的增大,耕作措施和生物措施Rrs呈减小趋势.Rrs较大的措施在减少相同的坡面侵蚀泥沙时,有利于增加土壤水分,但是不利于径流形成.     

黑土坡耕地横坡垄作对减少径流及土壤有机碳流失的作用

东北黑土坡耕地受土壤侵蚀和习惯顺坡耕作措施的影响,水土流失严重,土壤有机碳含量呈逐年下降趋势.针对东北黑土坡耕地不同垄作措施水土流失及土壤有机碳变化特征不明确的问题,采用田间定位试验的方法,探究了顺坡垄作和横坡垄作对坡耕地水土流失及土壤有机碳变化的影响.结果表明:(1)横坡垄作相对于顺坡垄作能显著减少径流总量97.1％...     

紫色土区小流域侵蚀产沙对水土保持措施的响应

探讨降雨量与水土保持措施对流域水沙关系的影响,对流域水土流失预报和水土保持效益评价具有十分重要的科学意义,但在紫色土区这方面的研究还相当薄弱。以鹤鸣观小流域Ⅱ号支沟实测降雨径流泥沙数据为基础,分析了水土保持措施对流域径流、泥沙及水沙关系的影响。结果表明:流域治理后期,降雨产流量变化率、降雨产沙量变化率均减小,随着降雨的增多,水土保持措施对径流、产沙的影响效应增强;暴雨强度愈小,降雨量愈少,水土保持径流拦蓄作用愈显著;但降雨量愈大,泥沙拦蓄作用愈显著;流域减水量一般在30%~70%,而减沙量都高于90%,减沙量明显高于减水量;由于水土保持综合治理的作用,1989年后的多年平均径流量较1989年前减少33.11%,多年平均产沙量减少90.50%。     

Effects of tillage and traffic on crop production in dryland farming systems: II. Long-term simulation of crop production using the PERFECT model

Soil water conservation is critical to long-term crop production in dryland cropping areas in Northeast Australia. Many field studies have shown the benefits of controlled traffic and zero tillage in terms of runoff and soil erosion reduction, soil moisture retention and crop yield improvement. However, there is lack of understanding of the long-term effect of the combination of controlled traffic and zero tillage practices, as compared with other tillage and traffic management practices.In this study, a modeling approach was used to estimate the long-term effect of tillage, traffic, crop rotation and type, and soil management practices in a heavy clay soil. The PERFECT soil–crop simulation model was calibrated with data from a 5-year field experiment in Northeast Australia in terms of runoff, available soil water and crop yield; the procedure and outcomes of this calibration were given in a previous contribution. Three cropping systems with different tillage and traffic treatments were simulated with the model over a 44-year-period using archived weather data.Results showed higher runoff, and lower soil moisture and crop production with conventional tillage and accompanying field traffic than with controlled traffic and zero tillage. The effect of traffic is greater than the effect of tillage over the long-term. The best traffic, tillage and crop management system was controlled traffic zero tillage in a high crop intensity rotation, and the worst was conventional traffic and stubble mulch with continuous wheat. Increased water infiltration and reduced runoff under controlled traffic resulted in more available soil water and higher crop yield under opportunity cropping systems.     

珠海城区暴雨径流污染负荷估算及其评价

基于对广东珠海城区暴雨径流污染的监测,引用SCS模型对城区暴雨径流污染负荷进行估算并分析评价。结果表明,珠海城区暴雨产流年平均1529.2mm,其中以交通主干道和商业区径流量最大。暴雨径流污染物浓度水平较高,T—N,T—P,COD_(Cr)和BOD_5负荷总量分别为765.27,74.06,11 958.94和1104.71t,其中COD_(Cr)负荷为工业点源污染的72.32％,占珠海非点源污染总负荷的24.69％。暴雨径流在雨后短时间内会使受纳水体的水质迅速恶化。因此,珠海城区暴雨径流对水环境的威胁较大。     

A Critical Review of the Water Balance and Agronomic Effects of Conservation Tillage under Rain‐fed Agriculture in Ethiopia

About 80% of Ethiopia's population is involved in rain‐fed agriculture. Moisture stress coupled with traditional tillage with breaking ard plough, locally known as ‘Maresha ’ are the major limiting factors for agricultural production. Soil erosion, low infiltration and decline agricultural productivity because of conventional tillage implement have been frequently reported. In order to curve this situation and meet the huge food demand of the growing population, different conservation tillage systems have been implemented. However, there is limited information about the impacts of the practices. This review paper therefore aimed at providing adequate information concerning the impacts of the practices on water balance and crop yield. Systematic, best evidence and narrative review techniques were used. Results revealed that the application of conservation tillage had brought significant improvement on water balance and agricultural production. Researchers found over 50% decreased in surface runoff, 9 to 40% improvement in water productivity and good crop transpiration (T = 53 mm season⁻¹), compared to conventional tillage T = 49 mm‐season⁻¹ because of conservation tillage implement. Moreover, doubled grain yield was obtained from ridging, subsoiling and wing plough (1076, 1044 and 1040 kg ha⁻¹, respectively) compared to traditional tillage which resulted in 540 kg ha⁻¹. Improving water balance and agricultural production in rain‐fed agriculture need to reduce evaporation and surface runoff through improving moisture retention and transpiration. This could be achieved by the adoption of conservation tillage which can improve on‐farm water balance, yields and water productivity among smallholder farmers in Ethiopia. Copyright © 2016 John Wiley & Sons, Ltd.